Light-emitting device and method for manufacturing the same

ABSTRACT

The present invention provides an organic light-emitting element where a lower electrode, an organic compound layer and an upper electrode are laminated on a substrate, wherein the upper electrode of the organic EL element is formed by a laminate of at least a conductive first inorganic film, a conductive organic film and a conductive second inorganic film, in order to suppress the occurrence of dark spot, so that the occurrence of pinholes in the upper electrode leading to dark spots is suppressed. Here, pinholes refer to holes in the upper electrode that penetrate upper electrode from the organic compound layer underneath to the atmosphere above.

This application is a continuation of application Ser. No. 11/417,815filed on May 3, 2006 now U.S. Pat. No. 7,488,985 which is a continuationof application Ser. No. 10/740,274 filed on Dec. 18, 2003 (now U.S. Pat.No. 7,045,822 issued May 16, 2006).

TECHNICAL FIELD

The present invention relates to a light-emitting device including alight-emitting element, where a layer that includes an organic compoundsuch as an organic electroluminescence (abbreviated below as EL)material is intervened between a pair of electrodes, and in particularto an electrode structure of the light-emitting element.

BACKGROUND ART

In recent years, the application, to next-generation flat paneldisplays, of light-emitting elements using an organic EL material havingcharacteristics such as thinness, light weight, high-speedresponsiveness and direct-current low-voltage driving has been expected.The light-emission mechanism of the light-emitting element is such thatan organic compound layer is sandwiched between a pair of electrodes anda voltage is applied thereto, whereby electrons implanted from a cathodeand holes injected from an anode are recombined at a light-emittingcenter in the organic compound layer to form molecular excitons, so thatthe molecular excitons release energy and emit light when they return tothe ground state. It is recognized that the biggest problem in utilizinglight-emitting elements using an organic EL material is improving theirreliability with the main purpose of extending their light-emittinglifetime.

It is thought that the reasons light-emitting elements using an organicEL element deteriorate are that the constituent material itselfdeteriorates due to applying an electric field thereto and driving thelight-emitting elements, and that the junction state at boundaries ofthe films configuring the light-emitting elements physically andchemically change. Also, even when the light-emitting elements aresimply stored without driving them, they end up deteriorating due toheat, moisture, oxygen, physical shock and sunlight from the outside.Among deterioration resulting from these external factors, deteriorationresulting from moisture and oxygen is particularly remarkable.

Dark spots are one example of a poor light-emission phenomenon oflight-emitting elements using an organic EL material, and arise due tomoisture and oxygen present in the atmosphere. Dark spots are aphenomenon where the light-emission luminance drops locally, and areobserved as tiny black spots present in the pixels at the stageimmediately after the fabrication of the light-emitting element. It isknown that dark spots, which are of a size that is initiallyimperceptible, grow by driving or storing over a long period of timelight-emitting elements using an organic EL material. The main causes ofdark spots are moisture and oxygen that penetrate the organic layerthrough holes (pinholes) formed in the upper electrode. FIG. 2 is anoptical microscope photograph of such a dark spot that is frequentlyobserved. FIG. 2 shows the presence of a dark spot 202 in a part (theregion encircled by the dotted line in the drawing) of pixels 201 wherelight-emitting elements using an organic EL material are arranged in amatrix.

FIG. 5 shows the cross-sectional structure of such a light-emittingelement, and schematically shows the reason dark spots arise. Referencenumeral 501 is a lower electrode, reference numeral 502 is an organiccompound layer, and reference numeral 503 is an upper electrode. Darkspots arise due to moisture and oxygen penetrating the organic compoundlayer through a pinhole 504 that is present in the upper electrode 503and penetrates the upper electrode 503 as far as the organic compoundlayer. It is thought that such pinholes arise due to foreign matter,unevenness of the lower electrode, unevenness resulting fromcrystallization of the organic material (particularly low Tg holetransport material) and crystal grain boundaries.

In an active matrix type light-emitting device, in order to form pixelswith thin film transistors (abbreviated below as TFT) and light-emittingelements, several layers of films are formed under the light-emittingelement, and there is the potential for foreign matter to adhere tothese films during each film-forming process and during conveyance ofthe substrate. Sometimes foreign matter also adheres to the substratesurface during the film formation of the lower electrode, the organiccompound layer and the upper electrode configuring the light-emittingelement. Pinholes form in the upper electrode surface if the upperelectrode does not completely cover surface unevenness resulting fromthe foreign matter (e.g., see Non-Patent Document 1).

Non-Patent Document 1

-   Synthetic Metals, Vol. 91, p. 113 (1997)

Spike-shaped bumps of several nm to several tens nm are present on thesurface of an ITO film frequently used as the lower electrode of alight-emitting element. The size of the bumps on the conductive ITO filmsurface is large, and the bumps can lead to point defects when the ITOand the upper electrode short-circuit, but they can also result in darkspots when they are of a size that will not short-circuit and are notcompletely covered by the upper electrode.

It is known that, for the above-described reasons, many pinholes arepresent in aluminum film commonly used as the upper electrode. It issaid that there are many pinholes in aluminum film formed by deposition,which is frequently used particularly because it does not damage theorganic layer during film formation.

Separation of the upper electrode and the organic layer is recognized asa mechanism where moisture penetrating through the pinholes triggers adrop in luminance (see Non-Patent Document 2), and sometimes themechanism of deterioration itself is dependent on the materialconfiguring the light-emitting element using an organic EL material, butthis mechanism is not completely understood.

Non-Patent Document 2

-   Applied Physics Letters, Vol. 77, No. 17, p. 2650 (2000)

As one example of a technique for reducing pinholes in the upperelectrode, a technique has been disclosed where a low-melting pointmetal is deposited on a metal electrode layer formed on an organiclight-emitting layer of an element using an organic EL material, and thedeposited metal is melted to form shield metal that fills in thepinholes in the metal electrode layer (e.g., see Patent Document 1).

Patent Document 1

-   Japanese Patent Laid-Open No. 2001-52863

DISCLOSURE OF THE INVENTION

However, in the method that deposits and melts a second electrode inorder to fill in pinholes present in the first electrode layer, theheating temperature necessary therefor becomes a problem. Indium,gallium, an alloy thereof, and an alloy of lead or aluminum and galliumare used for the metal for the second electrode, but the melting pointof gallium is 29° C., the melting point of indium is 154° C., and themelting point of lead is 327° C.

When a metal whose melting point is near room temperature, such asgallium, is used to form the second electrode, there is the potentialfor the electrode to become unstable due to the light-emitting elementgiving off heat as the light-emitting element is driven. When a materialwith a high melting point is used as the second electrode, there is thepotential for the light-emitting element to be damaged because it isnecessary to heat the element at a high temperature at the time theelectrode is formed. For example, the Tg of the hole transport layerusually has a low value of 60° C. to 150° C. When the light-emittingelement is heated at a temperature near Tg, the hole transport layercrystallizes and the stability of the element ends up being lost.

Thus, in order to reduce pinholes present in the upper electrode withoutdamaging the light-emitting element, an upper electrode forming methodis needed where it is not necessary to heat the element at a hightemperature and whose film properties do not become unstable at a lowtemperature.

In light of this problem, it is an object of the present invention tofabricate a highly reliable light-emitting element with which can beobtained high-quality light emission with no unevenness, even when theelement is stored for a long period of time, by suppressing theoccurrence of pinholes that lead to dark spots.

In order to solve this problem, in the present invention, an upperelectrode of a light-emitting device is formed by a laminate of at leasta conductive first inorganic film, a conductive organic film and aconductive second inorganic film, so that the occurrence of pinholes inthe upper electrode that lead to dark spots is suppressed. Here, theconductive inorganic films are metal films or transparent conductivefilms. Also, pinholes refer to holes in the upper electrode thatpenetrate upper electrode from the organic compound layer underneath tothe atmosphere above.

FIG. 1 shows a schematic diagram of the invention. Reference numeral 101is a lower electrode, reference numeral 102 is a layer including anorganic compound (also called an EL layer), reference numerals 103 to105 correspond to an upper electrode, with reference numeral 103 beingat least a conductive first inorganic film, reference numeral 104 beinga conductive organic film and reference numeral 105 being a conductivesecond inorganic film. Reference numerals 103 and 105 are configured byinorganic films in which pinholes arise, such as indicated by referencenumerals 106 and 107. However, the invention has a configuration thatcan block, with the conductive organic layer, the path of penetration ofmoisture and oxygen to the layer 102 including the organic compound.

Specifically, the conductive organic film 104 lengthens the path ofpenetration of moisture and oxygen between the pinhole 107 in theconductive second inorganic film and the pinhole 106 in the conductivefirst inorganic film and also fulfills a role as an absorbent. As aresult, the probability that moisture from the outside will pass throughthe pinhole 106 in the first inorganic film and reach the organiccompound layer 102 under the upper electrode is reduced. Thus, theprobability for dark spots to arise is reduced and higher quality imagedisplay is obtained. Also, by laminating a similar structure, the pathof penetration of moisture and oxygen to the organic compound layer islengthened, so that laminating several layers of the conductive organicfilm and the conductive inorganic films is also effective for preventingthe element from deteriorating.

The present invention is a light-emitting device comprising, on asubstrate including an insulating surface, a light-emitting element thatincludes a lower electrode, a layer including an organic compound thatcontacts the lower electrode, and an upper electrode that contacts thelayer including the organic compound, wherein the upper electrode isformed by sequentially laminating a conductive first inorganic film, aconductive organic film and a conductive second inorganic film.

The present invention is a light-emitting device where a light-emittingelement that includes a lower electrode, a layer including an organiccompound that contacts the lower electrode and an upper electrode thatcontacts the layer including the organic compound is sandwiched betweena first substrate and a second substrate, wherein the upper electrode ofthe light-emitting element disposed on the first substrate comprises aconductive first inorganic film, a conductive organic film and aconductive second inorganic film, and emission light from thelight-emitting element is transmitted and emitted through the secondsubstrate.

The present invention is also a light-emitting device where alight-emitting element that includes a lower electrode, a layerincluding an organic compound that contacts the lower electrode and anupper electrode that contacts the layer including the organic compoundis sandwiched between a first substrate and a second substrate, whereinthe upper electrode of the light-emitting element disposed on the firstsubstrate is configured a conductive first inorganic film, a conductiveorganic film and a conductive second inorganic film, and emission lightfrom the light-emitting element is transmitted and emitted through thefirst substrate.

In the present invention, the upper electrode of the light-emittingelement can be one where the first inorganic film and the secondinorganic film are formed by a metal, or one where the first inorganicfilm and the second inorganic film are formed by a transparentconductive film or a laminate of a thin metal film and a transparentconductive film.

The first inorganic film can be formed by a material including an alkalimetal or an alloy or compound including an alkali metal or an alkalineearth metal or an alloy or compound including an alkaline earth metal.Alternatively, the first inorganic film can be formed by a materialincluding a first layer including an alkali metal or an alloy orcompound including an alkali metal and a second layer comprising aconductive material having a higher work function than that of thealkali metal or the alloy or compound including an alkali metal.

Also, an organic film may be hygroscopic, and is preferably formed by aconductive resin film. As another embodiment, the organic film mayinclude an alkali metal or an alkaline earth metal, or an alkali metal,an alkaline earth metal and a transition metal including a rare earthmetal. The organic film may also be translucent.

As an embodiment of the upper electrode, it is preferable for endsurfaces of the organic film to be covered by the second inorganic film.

The present invention is also a manufacturing method of a light-emittingdevice comprising, on a substrate including an insulating surface, alight-emitting element that includes a thin film transistor, a lowerelectrode, a layer including an organic compound that contacts the lowerelectrode and an upper electrode that contacts the layer including theorganic compound, the method comprising: a first step of forming thelower electrode contacting the thin film transistor on the substrate; asecond step of forming the layer including the organic compound on thelower electrode; and a third step of forming the upper electrode on thelayer including the organic compound, wherein the third step of formingthe upper electrode includes a first substep of forming a conductivefirst inorganic film, a second substep of forming a conductive organicfilm on the first inorganic film and a third substep of forming aconductive second inorganic film on the organic film. In the secondsubstep, the organic film is formed by coating or deposition.

According to the present invention, a light-emitting device without darkspots can be completed. As a result, a highly reliable light-emittingdevice can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing means for solving the problem.

FIG. 2 is a microscopic photograph of a dark spot.

FIG. 3 are diagrams showing an example of a process representing anembodiment mode.

FIG. 4 are a top view and a cross-sectional view showing Embodiment 1.

FIG. 5 is a schematic diagram showing a conventional light-emittingelement.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment mode of the invention is described in detail below usingthe drawings. Although it is possible to implement the invention in manydifferent aspects, here, as one representative mode, an example isdescribed below where a cathode and a layer including an organiccompound are formed on an active matrix substrate where anodes (ITO)connected to a TFT are arranged in a matrix.

Embodiment Mode 1

As shown in FIG. 3(A), a base film 301 is formed on a substrate 300including an insulating surface. Next, a TFT is formed. An anode (pixelelectrode) 310 connected to a drain electrode or a source electrode 308and 307 of the TFT is formed. A metal with a large work function (Pt,Cr, W, Ni, Zn, Sn, In) is used as the anode. In the present embodiment,a conductive film comprising ITO formed by sputtering is used. The TFTcomprises a gate electrode 305, a channel forming region 302, a sourceregion or a drain region 303 and 304, the drain electrode or the sourceelectrode 308 and 307, and insulating films 306 a and 306 b. Here, ap-channel type TFT, which is a semiconductor film (representatively, apolysilicon film) where the channel forming region is a crystallinestructure, is described as an example of the TFT.

The uppermost layer of the interlayer insulating film of the TFT, i.e.,the insulating layer 306 b contacting the lower surface of the anode 310is an inorganic insulating film (representatively, a silicon nitridefilm formed by radio-frequency (RF) sputtering). By disposing aninorganic insulating film with excellent coverage, cracks in the anodeformed thereabove can be eliminated. Also, by using an inorganicinsulating film, the moisture absorbed at the surface can be reduced.

The silicon nitride film formed by RF sputtering is a fine film usingsilicon as a target, the speed of etching using LAL500 is 0.77 nm/min to8.6 nm/min, which is slow, and the hydrogen concentration in the film is1×10²¹ atoms/cm³ as measured by secondary ion mass spectrometry (SIMS).By LAL500 is meant “LAL500 SA buffered hydrofluoric acid” made byHashimoto Chemical Co., Ltd., and is an aqueous solution ofNH₄HF₂(7.13%) and NH₄F (15.4%). Also, with the silicon nitride filmformed by RF sputtering, there is almost no difference in the shift ofC-V characteristics before and after a BT stress test, and alkali metalsand impurities can be blocked.

Also, by using an organic resin film as the interlayer insulating film306 a, flatness can be improved. When a silicon oxide film, a siliconoxynitride film or a silicon nitride film formed by plasma CVD orsputtering is used instead of an organic resin film, the occurrence of anon-light-emitting region immediately after manufacturing thelight-emitting element and expansion of the non-light-emitting regionsdo not arise, and cracks in the anode can also be eliminated.

Next, dividers 311 that cover end portions of the anode 310 are formed.The dividers 311 are formed to cover the contact holes of the TFT and awiring 309, and to maintain the insulation between adjacent pixels andthe wiring. An inorganic material (silicon oxide, silicon nitride,silicon oxide nitride, etc.), a photosensitive or non-photosensitiveorganic material (polyimide, acryl, polyamide, polyimideamide, a resist,or benzocyclobutene), or a laminate of these can be used for thedividers 311, but here a photosensitive organic resin is used. Forexample, when a positive-type photosensitive acryl is used as thematerial of the organic resin, it is preferable to impart a curvedsurface having a curvature radius at only the upper end portion of theinsulator. A negative type that becomes insoluble in the etchant due tophotosensitive light and a positive type that becomes soluble in theetchant due to light can both be used.

Also, the dividers 311 may be covered with a protective film comprisingan aluminum nitride film, an aluminum oxynitride film or a siliconnitride film. By covering the dividers 311 with a protective filmcomprising an inorganic resin film, the moisture absorbed at the surfacecan be reduced. When the interlayer insulating film is an organicmaterial, moisture penetrating the panel through the interlayerinsulating film can be prevented from penetrating the organic compoundlayer.

Next, the surface of the anode 310 is cleaned. Here, in order to removemicro-grains present on the surface of the anode, the anode surface isscrubbed and cleaned with a porous sponge (representatively, made of PVA(polyvinyl alcohol) or nylon) containing a surfactant (weakly alkaline).By scrubbing and cleaning the anode surface, point defects resultingfrom micro-grains and dark spots can be reduced, and the abnormalitywhere light emission efficiency drops extremely when the element isdriven with a low voltage (3 V to 5 V) can be eliminated. Here, anexample was described where the anode was cleaned after the dividers 311were formed, but the anode may also be cleaned before the dividers 311are formed or both before and after the dividers 311 are formed.

Also, a layer including an organic compound 312 is formed usingdeposition or coating. In order to improve reliability, it is preferableto conduct vacuum heating (100° C. to 250° C.) and conduct deaerationimmediately before the layer 312 including the organic compound isformed. For example, when deposition is used, deposition is conducted inan evacuated film-forming chamber whose degree of vacuum is 5×10⁻³ Torr(0.665 Pa) or less and preferably 10⁻⁴ to 10⁻⁶ Pa. At the time ofdeposition, the organic compound is first gasified by resistance heatingand then dispersed in the direction of the substrate due to a shutteropening at the time of deposition. The gasified organic compound isdispersed upwards, passes through an open portion disposed in a metalmask and is deposited on the substrate. A polymer material, alow-molecular weight material, an inorganic material, a layer in whichthese are mixed, a layer in which these are dispersed, or a laminate inwhich these layers are appropriately combined may be used as the layer312 including the organic compound.

Reference numeral 313 is a cathode first layer. As the conductiveinorganic film forming the cathode first layer, it is preferable toselect a material that is stable and whose electron donating property toan underlayer electron transporting layer and an electron injectinglayer is high, i.e., whose work function is low. An alloy of an alkalimetal or alkaline earth metal and a non-corrosive metal such as aluminumcan be used as the material. A laminate film of alloys of these and anon-corrosive metal or an alloy thereof may also be used. Depending onthe selection of the electron injecting layer, aluminum, a metal with ahigher work function than that of aluminum and an alloy thereof can beused directly on the electron injecting layer. A laminate film thereofcan also be used. The material used for the cathode first layer is notlimited to these as long as it is a material whose electron donatingproperty to the layer 312 including the organic compound of theunderlayer is high. Also, if the element is an upper surface emissiontype or both surfaces emission type, a thin metal film, a transparentconductive film, or a laminate thereof can be used for the cathode.

With respect to the film-forming method of the cathode first layer, itis preferable to conduct deposition using resistance heating or to usesputtering because, in deposition using an electron beam, the TFT isdamaged by X-rays emitted at the time of deposition.

A conductive organic material is used as a cathode second layer 314. Itis preferable for the conductive organic material to be a highlyhygroscopic material in order to suppress moisture passing throughpinholes in a cathode third layer and penetrating the cathode secondlayer from penetrating the cathode first layer. In the presentembodiment mode, it is preferable to use a material whose electrontransportation property is high as the conductive organic materialbecause the upper electrode is a cathode. The conductive organicmaterial forming the cathode second layer can be doped with an alkalimetal, an alkaline earth metal or a transition metal such as a rareearth metal in order to improve the conductivity of the organic materialand improve electrical contact with the inorganic material.

For the cathode second layer, it is preferable to form a film of aconductive resin by coating. By coating is meant spin-coating, spraying,screen printing or painting. By applying a conductive resin as theorganic compound of the second layer, not only pinholes resulting fromcrystal grain boundaries but also pinholes present in the cathode of thefirst layer resulting from base unevenness and foreign matter can becovered and the surface of the second layer can be flattened. With thismethod, pinholes resulting from foreign matter, base unevenness andcrystal grain boundaries can be reduced in the cathode overall, and itis possible to prevent dark spots from arising. Also, because thecathode surface is flattened, coverage when conducting film sealingabove the element becomes better.

A depositable organic material can also be used as the cathode secondlayer. In particular, it is possible to use the same material as thatused for the layer 312 including the organic compound. Coverage withrespect to foreign matter and ITO unevenness is not as good as that of acoated film, but pinholes resulting from crystal grain boundaries arereduced by using an amorphous film with no pinholes. By using an organicfilm that has good coverage with respect to unevenness in this case, itis possible to also reduce dark spots resulting from foreign matter andITO unevenness.

In the case of an upper surface light-emitting element, it is preferablefor the cathode of the second layer to be transparent in the visiblelight region.

As a third layer cathode 315, it is preferable to use aluminum or amaterial that is more difficult to oxidize than aluminum (high workfunction). Aluminum or the material that is more difficult to oxidizethan aluminum may be used singly or an alloy thereof may be used. It isalso possible to use a laminate film of these. The material used for thecathode third layer is not limited to the above materials.

The cathode of the third layer is preferably formed so that end surfacesof the conductive organic material of the second layer are covered inorder to prevent moisture and oxygen from penetrating those end portionsto the pixel portion. If an insulating passivation film is present onthe cathode, the end surfaces of the organic layer of the second layermay be covered with the passivation film.

It is preferable to form the cathode of the third layer with sputteringthat can form a fine film. The third layer cathode can also be formedusing deposition.

Due to the above processes, a light-emitting element in which there areno dark spots, and in which luminance deterioration resulting frommoisture, such as luminance deterioration from the pixel periphery orluminance deterioration from the panel periphery, is suppressed, can beformed.

EMBODIMENT Embodiment 1

The configuration of an active matrix type light-emitting device inwhich a TFT is disposed on each pixel is described as an embodiment ofthe invention. FIG. 4(A) is a top view thereof and FIG. 4(B) is across-sectional view cut along chain line A-A′.

In FIG. 4(A), reference numeral 1 is a source signal line drivingcircuit, reference numeral 2 is a pixel portion and reference numeral 3is a gate signal line driving circuit. Also, reference numeral 4 is asealing substrate, reference numeral 5 is a sealant, and the inner areasurrounded by the sealant 5 serves as a space filled with an inert gasdried by a desiccant (not shown). Reference numeral 7 is a connectionregion where an upper electrode shared by light-emitting elements isconnected to wiring on the substrate.

Video signals and clock signals are received from an FPC (flexibleprinted circuit) 6 serving as an external input terminal. Here, only theFPC is shown, but a printed wiring board (PWB) may also be attached tothe FPC. The light-emitting device in this specification includes notonly a main body of the light-emitting device but also a deviceincluding a state where an FPC or PWB is attached thereto.

Next, the cross-sectional structure is described using FIG. 4(B).Driving circuits and pixel portions are formed on a substrate 10, buthere the pixel portion 2 and the connection region 7 are shown. Also, inthe present embodiment, a configuration is shown where a base film 11that prevents pollutants from the substrate is disposed on the substrate10, but it is not invariably necessary to dispose the base film 11.

The pixel portion 2 is formed by plural pixels including a switchingtransistor TFT 70, a capacitor 41, a current control TFT 50 connected toa first electrode, and a first electrode (anode) 28 a serving as a lowerelectrode electrically connected to a drain region or a source region(high-density impurity regions) 62 b of the current control TFT 50.Plural TFTs are formed on one pixel. In FIG. 4(B), an example using ap-channel type TFT that includes an upper layer 66 b of a gate electrodeand a channel forming region 62 a that are superposed with a gateinsulating film 15 sandwiched therebetween, a lower layer 66 a of thegate electrode and low-density impurity regions 62 d that are superposedwith the gate insulating film 15 sandwiched therebetween, andlow-density impurity regions 62 c that are not superposed with the lowerlayer 66 a of the gate electrode is shown for the current control TFT50, but the current control TFT 50 is not limited thereto. An n-channeltype TFT may also be used. One of the reference numerals 23 and 24 is asource electrode, and the other is a drain electrode, and 24 also is aconnection electrode that connects the first electrode 28 a and thehigh-density impurity regions 62 b.

FIG. 4(B) shows a cross-sectional view of the current control TFT 50,the switching TFT 70 and the capacitor 41. In FIG. 4, an example using,for the switching TFT 70, an n-channel type TFT including plural channelforming regions 60 a superposed with the gate electrodes 64, with thegate insulating film 15 sandwiched therebetween, is shown, but theswitching TFT 70 is not limited thereto. A p-channel type TFT may alsobe used. One of the reference numerals 47 and 48 is a source wiring, andthe other is a drain wiring, 60 b is a source region or a drain region,60 c are low-density impurity regions that are not superposed with thegate electrodes 64, and 60 d are low-density impurity regions superposedwith the gate electrodes 64. With respect to the capacitor 41, aretention capacity is formed by an electrode 46 and an electrode 63using interlayer insulating films 20 and 22 as dielectrics, and aretention capacity is formed by the electrode 63 and a semiconductorfilm 42 using the gate insulting film 15 as a dielectric.

For the interlayer insulating films 20, 21 and 22, a photosensitive ornon-photosensitive organic material (polyimide, acryl, polyamide,polyimideamide, a resist or benzocyclobutene), an inorganic material(silicon oxide, silicon nitride, silicon oxynitride, etc.) formed bysputtering, CVD or coating, or a laminate of these can be used.

In FIG. 4, an inorganic insulating film 20 comprising silicon nitride isdisposed so as to cover the gate electrode and the gate insulating film15. The inorganic insulating film 20 is an inorganic insulating filmthat is disposed for hydrogenation to terminate dangling bonds of thesemiconductor layer by conducting film formation with the condition thathydrogen is included in the film and conducting heating. Thesemiconductor layer present underneath can be hydrogenated withoutrelation to the presence of the gate insulating film 15 comprisingsilicon oxide. Also, after a film of a photosensitive organic materialis formed by coating to form the interlayer insulating film 21, theinterlayer insulating film 21 is selectively etched by wet etching ordry etching so that the upper end portion thereof becomes a curvedsurface having a curvature radius. When an organic material is used asthe interlayer insulating film 21, it is preferable to cover theinterlayer insulating film 21 with an interlayer insulating film 22comprising a silicon nitride film, a silicon oxide nitride film, analuminum oxynitride film or a laminate of these to block the interlayerinsulating film 21 so that moisture, gas or impurities from within theinterlayer insulating film 21 are not diffused and do not cause thelight-emitting element formed thereafter to deteriorate. The interlayerinsulating film 22 can also block the diffusion of impurities from thesubstrate 10 to the light-emitting element and block the diffusion ofimpurities from the light-emitting element to the TFTs. When ahygroscopic organic material is used as the interlayer insulating film21, it is necessary to rebake the organic material because it swellswhen it is exposed to a solution such as a stripper used in otherpatterning in a later process, but the interlayer insulating film 21 canbe prevented from swelling by covering it with the interlayer insulatingfilm 22.

Also, the order in which the interlayer insulating films are laminatedand the process order are not limited to the order in which theinterlayer insulating films shown in FIG. 4 are laminated or the processorder of film formation and hydrogenation. For example, the interlayerinsulating film 21 that prevents the diffusion of impurities may beformed on an interlayer insulating film for hydrogenation andhydrogenated, then a film of an organic resin material may be formed bycoating, and the interlayer insulating film 22, whose upper end portionis formed by wet etching or dry etching as a curved surface having acurvature radius, may be formed. It is preferable to etch the organicresin film by wet etching because, when a film comprising an organicresin is dry-etched, a charge arises and there is the potential to alterthe TFT characteristics. When an interlayer insulating film comprising alaminate of an inorganic insulating film and an organic resin film isetched, only the organic resin film is wet-etched, or the inorganicinsulating film is dry-etched and then the organic resin film is formedand wet-etched.

When a photosensitive organic resin material is used as the interlayerinsulating film 21, it is easy to form the curved surface having acurvature radius at the upper end portion as shown in FIG. 4, but anon-photosensitive organic resin material or inorganic material is usedas the interlayer insulating film 22.

Also, because the present embodiment is a case where the light-emittingdevice is an undersurface emission type, it is preferable to use atransparent material for the interlayer insulating films 20 to 22.

Insulators (also called banks, dividers, barriers, mound, etc.) 30 areformed at both ends of the first electrode (anode) 28 a, and a layer(also called an EL layer) 31 including an organic compound is formed onthe first electrode (anode) 28 a. At the time of deposition, the organiccompound is first gasified by resistance heating and then dispersed inthe direction of the substrate due to a shutter opening at the time ofdeposition. The gasified organic compound is dispersed upwards, passesthrough an open portion disposed in a metal mask and is deposited on thesubstrate so that the layer 31 including the organic compound serving asa light-emitting layer (including a hole transporting layer, a holeinjecting layer, an electron transporting layer, an electron injectinglayer) is formed. Because the layer 31 including the organic compound isextremely thin, it is preferable for the surface of the first electrodeto be flat. For example, planarization may be conducted, beforepatterning or after patterning of the first electrode, by a process thatchemically and mechanically polishes (representatively, the CMPtechnique) the surface of the first electrode. When CMP is conducted,the flatness of the first electrode can be further improved byconducting CMP to thin the film thickness of the electrode 24 or theinsulators 30 or to give the end portions of the electrode 24 taperedshapes. When an organic resin film is used as the interlayer insulatingfilm 21, in order to improve the flatness of the first electrode (anode)28 a, it is preferable to dispose an inorganic insulating film as theinterlayer insulating film 22 to prevent the occurrence of cracks andsuppress the occurrence of a non-light-emitting region immediately aftermanufacturing and the occurrence of point defects. Also, in order toimprove the cleanliness of the surface of the first electrode, cleaning(brush cleaning or sponge cleaning) for cleaning off foreign matter isconducted before and after the formation of the insulators 30, so thatthe occurrence of dark spots and point defects are reduced.

As the first electrode (anode) 28 a, a transparent conductive film (ITO(indium oxide tin oxide alloy), an indium oxide zinc oxide alloy(In₂O₃—ZnO), a zinc oxide (ZnO), etc.) may be used.

Also, as the insulators 30, a photosensitive or non-photosensitiveorganic material (polyimide, acryl, polyamide, polyimideamide, a resistor benzocyclobutene), an inorganic material (silicon oxide, siliconnitride, silicon oxynitride, etc.) formed by CVD, sputtering or coating,or a laminate of these can be used. Also, when a photosensitive organicmaterial is used as the insulators 30, the photosensitive organicmaterial can be broadly divided into two types—a negative type thatbecomes insoluble in the etchant due to photosensitive light and apositive type that becomes soluble in the etchant due to light—but bothcan be appropriately used.

When a negative-type photosensitive organic material is used as theinsulators 30, it is easy to form the curved surface having a curvatureradius at the upper end portion thereof, but when a positive-typephotosensitive organic material is used, it becomes the cross-sectionalshape of the insulators. Also, when the insulators 30 comprise anorganic material, the insulators 30 may be covered with an inorganicinsulating film (a silicon nitride film formed by sputtering, etc.).

Also, when an organic material is used as the insulators 30 or theinterlayer insulating films 20 to 22, it is important to conduct heatingin a vacuum and conduct deaeration in order to remove gas and moisturein the films, and it is preferable to conduct vacuum heating at 100° C.to 250° C. immediately before forming the layer 31 including the organiccompound.

Also, when inorganic insulating films are used as the interlayerinsulating films 20 to 22, the films may be formed using plasma CVD orsputtering. In particular, with a silicon nitride film where silicon isused as a target in RF sputtering, where the substrate temperature isroom temperature to 350° C., where the film-forming pressure is 0.1 Pato 1.5 Pa, and where high-frequency power (5 to 20 W/cm²) of 13.56 MHzis applied so that the silicon nitride film is formed by only nitrogengas or a mixed gas of nitrogen gas and argon gas, the blocking effectwith respect to Na, Li and other elements belonging to Group 1 or Group2 of the Periodic Table is extremely strong, and the diffusion of thesemovable ions and the like can be effectively suppressed. A metal filmwhere 0.2 to 1.5 wt % (preferably 0.5 to 1.0 wt %) of lithium is addedto aluminum is preferable for the cathode first layer used in thepresent embodiment with respect to the electron injecting property orfor the rest. When a material including lithium is used as the cathode,there is the potential for the operation of the transistor to beadversely affected by the diffusion of the lithium, but lithium can beprevented from being diffused in the TFT if the material is a siliconnitride film formed by RF sputtering.

When the layer 31 including the organic compound is used as a full-colordisplay, material layers specifically emitting red, green and blue lightmay be appropriately and selectively formed by deposition using adeposition mask or ink-jetting. When a layer including an organiccompound 31 that emits green light is formed, in the present embodiment,a 60 nm α-NPD film is formed, a 40 nm Alq₃ film to which DMQD has beenadded is formed as a green light-emitting layer using the samedeposition mask, a 40 nm Alq₃ film is formed as an electron transportinglayer, and a 1 nm CaF₂ film is formed as an electron injecting layer.Also, when a layer including an organic compound 31 that emits bluelight is formed, a 60 nm α-NPD film is formed, a 10 nm BCP film isformed as a blocking layer using the same mask, a 40 nm Alq₃ film isformed as an electron transporting layer, and a 1 nm CaF₂ film is formedas an electron injecting layer. Also, when a layer including an organiccompound 31 that emits red light is formed, a 60 nm α-NPD film isformed, a 40 nm Alq₃ film to which DCM has been added is formed as a redlight-emitting layer using the same mask, a 40 nm Alq₃ film is formed asan electron transporting layer, and a 1 nm CaF₂ film is formed as anelectron injecting layer.

Also, for white light emission, the device may be configured as alight-emitting display device with which full-color display is possibleby separately disposing a color filter and a color conversion layer.When the device is to be used as a display device conducting only simpledisplay or as an illumination device, the device can be configured toemit light of a single color (representatively, white light). Forexample, an electron-transporting 1,3,4-oxadiazole derivative (PBD) maybe dispersed in hole-transporting polyvinylcarbazole (PVK). Also, whitelight emission can be obtained by dispersing 30 wt % of PBD as anelectron-transporting agent and appropriately dispersing 4 types ofpigments (TPB, coumarin 6, DCM 1, Nile red). It is also possible toobtain white light emission overall by appropriately selecting anorganic compound film that emits red light, an organic compound filmthat emits green light and an organic compound film that emits bluelight, and superposing and mixing the colors.

Also a poly(ethylenedioxythiophene)/poly(styrene sulfonate) aqueoussolution (PEDOT/PSS), a polyaniline/camphor sulfonic acid aqueoussolution (PANI/CSA), PTPDES, Et-PTPDEK or PPBA acting as a holeinjecting layer (anode buffering layer) may be applied to the entiresurface of the first electrode (anode) 28 a and calcinated. When a holeinjecting layer comprising a polymer material is formed by a coatingmethod such as spin-coating, the flatness is improved, and the coverageand uniformity in film thickness of a film formed thereon can be madeexcellent. In particular, because the film thickness of thelight-emitting layer becomes uniform, uniform light emission can beobtained. In this case, it is preferable to conduct vacuum heating (100to 200° C.) immediately before film formation by deposition after thehole injecting layer has been formed by coating. For example, after thesurface of the first electrode (anode) has been cleaned with a sponge, apoly(ethylenedioxythiophene)/poly(styrene sulfonate) aqueous solution(PEDOT/PSS) is coated on the entire surface of the first electrode to afilm thickness of 60 nm, pre-calcinated at 80° C. for 10 minutes,calcinated at 200° C. for 1 hour, and then vacuum-heated (heated at 1700for 30 minutes and then cooled for 30 minutes) immediately prior todeposition, to form a light-emitting layer by deposition without cominginto contact with the atmosphere. Particularly when unevenness andmicroparticles are present on the film surface of ITO, the affectsthereof can be reduced by thickening the film thickness of thePEDOT/PSS.

Also, because the wettability of PEDOT/PSS is not very good when it isapplied to the ITO film, it is preferable to improve the wettability byapplying the PEDOT/PSS solution a first time by spin-coating and thencleaning the surface of the electrode with pure water, then againapplying the PEDOT/PSS solution a second time by spin-coating, andconducting calcination to form a uniform film. The effects that thesurface is modified by cleaning it with pure water after the firstcoating and microparticles can also be removed can be obtained.

Also, when a PEDOT/PSS film is formed by spin-coating, it is preferableto selectively remove end surfaces and peripheral portions of thesubstrate, terminal portions and connection regions between the cathodeand the wiring underneath because the PEDOT/PSS is formed on the entiresurface, and it is preferable to remove these with O₂ ashing.

Also, cathodes 32, 33 and 34 serving as an upper electrode are formed onthe layer 31 including the organic compound. In order to reduce thenumber of pinholes resulting in dark spots, the cathodes are formed bylaminating the layer 32, which comprises a conductive inorganicmaterial, the layer 33, which comprises a conductive organic material,and the layer 34, which comprises a conductive inorganic material.

It is preferable for the conductive inorganic material forming thecathode first layer 32 to be a material whose electron donating propertyto the electron transporting layer and electron injecting layer is highand whose physical junction with the electron transporting layer and theelectron injecting layer is excellent. Examples of metals that have alow work function and are stable include alkali metals and alkalineearth metals such as lithium, indium, magnesium, strontium, calcium,potassium, sodium and barium, and alloys with metals having a largerwork function than that of aluminum such as aluminum and silver. Alloysof these and aluminum and metals having a larger work function than thatof aluminum may also be laminated. In a case where excellent electricalcontact with the organic compound layer is possible even if a metal notincluding an alkali metal or an alkaline earth metal is used for thecathode first layer, such as a case where the electron injection layeris doped with an alkali metal or an alkaline earth metal, anon-corrosive metal comprising aluminum, silver, iron, chromium, nickel,gallium, molybdenum, platinum, gold, carbon, iron, antimony, tin,tungsten, zinc, ruthenium, cadmium, tantalum, cobalt, arsenic, niobium,palladium and bismuth can be used. Also, alloys of these metals andlaminates can be used. In the present embodiment, excellent EL elementcharacteristics can be obtained even if a material having a relativelyhigh work function is used as the first layer cathode because CaF₂ isused for the electron injecting layer. Here, aluminum is used as thecathode of the first layer.

Also, if the element is an upper surface emission type element, atransparent conductive film (ITO (indium oxide tin oxide alloy), anindium oxide zinc oxide alloy (In₂O₃—ZnO), a zinc oxide (ZnO), etc.) ora laminate of a transparent conductive film and a thin metal film can beused for the cathode first layer.

With respect to the film-forming method of the cathode first layer, itis preferable to conduct deposition using resistance heating or to usesputtering because, in deposition using an electron beam, the TFT isdamaged by X-rays emitted at the time of deposition. Also, it ispreferable for the deposition rate to be high when the cathode firstlayer is deposited using resistance heating. Because the kinetic energyof the substance being deposited is high, a finer film can be formed.Also, a finer film can be formed by forming the film using ion assistdeposition. The cathode material of the first layer is not limited tothe example given above, and it is possible to use various metals andalloys thereof.

Any material can basically be used to form the cathode second layer 33as long as the material is a conductive organic material. However, inconsideration of the ease of the film formation method, conductive resinsuch as poly(ethylenedioxythiophene)/poly(styrene sulfonate) aqueoussolution (PEDOT/PSS), and polyvinyl carbazole (PVK), or an amorphousdepositable material such as Alq3 or α-NPD used in EL layers ispreferable. These material films are hygroscopic and substantiallytransparent if the film thickness is thin. In the present embodiment, itis preferable to use a material having high electron transportability asthe conductive organic material because the upper electrode is used as acathode. The conductive organic material can be doped with an alkalimetal or alkaline earth metal such as lithium, indium, magnesium,strontium, calcium, potassium, sodium and barium, or a transition metalsuch as a rare earth metal, in order to improve the conductivity of theorganic material and improve electrical contact with the inorganicmaterial.

For the upper electrode second layer, it is preferable to form a film ofa conductive resin by coating. By coating is meant spin-coating,spraying, screen printing or painting. By applying a conductive resin asthe cathode second layer, not only pinholes resulting from crystal grainboundaries but also pinholes in the cathode resulting from baseunevenness and foreign matter can be reduced and the cathode surface canbe flattened. With this method, it is possible to suppress theoccurrence of dark spots resulting from foreign matter and unevenness ofthe base. Also, it is thought that, because the cathode surface isflattened, coverage when conducting film sealing above the elementbecomes better. When a film of the conductive organic material is formedusing coating, it is preferable to calcinate the film by vacuum heatingafter film formation.

An organic material that is depositable and conductive, such as Alq₃,α-NPD or BCP, can be used as the cathode of the second layer. Coveragewith respect to foreign matter and ITO unevenness is not as good as thatof a coated film, but pinholes resulting from crystal grain boundariesare reduced by using an amorphous film with no pinholes. By using anorganic film that has good coverage in this case, it is possible to alsoreduce dark spots resulting from foreign matter and ITO unevenness. Alsoby using a conductive organic material other than the above, it ispossible to reduce the number of pinholes.

In the case of an upper surface light-emitting element, it is necessaryfor the cathode of the second layer to be transparent in the visiblelight region.

As the cathode 34 of the third layer, it is preferable to use aluminumor a material having a higher work function than that of aluminum.Aluminum and the material having a higher work function than that ofaluminum may be used singly or an alloy thereof may be used. It is alsopossible to use a laminate film of these.

It is preferable to form the cathode of the third layer by sputteringthat can form a fine film. The cathode of the third layer can also beformed using deposition. When the cathode of the third layer is formed,it is preferable to form the film so that the end surfaces thereof arecovered in order to prevent water and oxygen from penetrating the pixelportion from the end surfaces of the conductive organic material of thesecond layer. If a passivation film is present on the cathode, the endsurfaces of the organic layer of the second layer may also be coveredwith the passivation film.

Thus, a light-emitting element comprising the first electrode 28 a, thelayer including the organic compound 31 and the second electrodes 32, 33and 34 is formed. When the light-emitting element is an undersurfaceemission type, a color filter (here, unillustrated) comprising acoloring layer and BM is disposed on the substrate 10.

The second electrodes 32, 33 and 34 also function as wirings shared withall pixels and are electrically connected to the FPC 6 via the wirings.In FIG. 4, the connection region 7 that connects the wiring 45 to thesecond electrodes 32, 33 and 34 is shown, and this wiring is pulledaround and electrically connected to the FPC.

Also, with respect to the terminal portions, a terminal electrodecomprising a laminate of an electrode formed by the same process as thegate electrode, an electrode formed by the same process as the sourceelectrodes or the drain electrodes and an electrode formed by the sameprocess as the first electrode 28 a is adhered to the FPC 6 with anadhesive such as a conductive adhesive. The configuration of theterminal portions is not particularly limited and may be appropriatelyformed.

The sealing substrate 4 is adhered with the sealing agent 5 including afiller in order to seal the light-emitting element formed on thesubstrate 10. A spacer comprising a resin film may also be disposed inorder to secure an interval between the sealing substrate 4 and thelight-emitting element. Additionally, the space inside the sealing agent5 is filled with an inert gas such as nitrogen. It is preferable to usean epoxy resin as the sealing agent 5. It is also preferable for thesealing agent 5 to be a material that does not transmit moisture oroxygen as much as possible. Moreover, a material (desiccant, etc.)having the effect of absorbing oxygen and water may be disposed insidethe space.

Also, in the present embodiment, other than a glass substrate or quartzsubstrate, a plastic substrate comprising FRP (Fiberglass-ReinforcedPlastics), PVF (polyvinyl fluoride), Mylar, polyester or acryl and thelike can be used as the material configuring the sealing substrate 4. Itis also possible to seal with a sealing agent so as to cover the sidesurfaces (exposure surfaces) after the sealing substrate 4 has beenadhered with the sealing agent 5.

By sealing the light-emitting element in a closed space as describedabove, the light-emitting element can be completely blocked from theoutside, and substances that promote the deterioration of the organiccompound layer, such as moisture and oxygen, can be prevented frompenetrating from the outside.

Also, the present invention is not limited to the configuration of theswitching TFT of the pixel portion of FIG. 4. For example, just the LDDregions 60 c that do not overlap with the gate electrode may bedisposed, via a gate insulating film, between the channel forming region60 a and the drain region (or the source region) 60 b. The gateelectrode shape is also not limited and may be a single-layer gateelectrode.

Here, the invention was described using a top-gate type TFT as anexample, but the invention can be applied without relation to a TFTstructure. For example, it is possible to apply the invention to abottom gate type (an inversely staggered type) TFT or a staggered typeTFT.

Also, in FIG. 4, a configuration was described where the first electrode28 a was formed after the connection electrode 24 connected to thesource region or the drain region was formed, but the invention is notparticularly limited. For example, the connection electrode connected tothe source region or the drain region may also be formed after the firstelectrode. An interlayer insulating film that covers the electrodeconnected to the source region or the drain regions may further bedisposed and a contact hole may be formed, and thereafter the firstelectrode connected to the electrode may be formed on the interlayerinsulating film.

The source signal line driving circuit 1 that drives the EL element canbe manufactured in the same manner as the pixel portion so that a CMOScircuit is formed where an n-channel type TFT and a p-channel type TFTare combined. The n-channel type TFT includes a gate electrode of anupper layer and a channel forming region that are superposed with a gateinsulating film sandwiched therebetween, a gate electrode of a lowerlayer and low-density impurity regions that are superposed with the gateinsulating film sandwiched between, low-density impurity regions thatare not superposed with the gate electrode of the lower layer, andhigh-density impurity regions serving as a source region or a drainregion.

Also, the p-channel type TFT includes a gate electrode of an upper layerand a channel forming region that are superposed with a gate insulatingfilm sandwiched therebetween, a gate electrode of a lower layer andlow-density impurity regions that are superposed with the gateinsulating film sandwiched therebetween, low-density impurity regionsthat are not superposed with the gate electrode of the lower layer, andhigh-density impurity regions serving as a source region or a drainregion. Also, the TFT forming the drive circuit may also be formed by aknown CMOS circuit, PMOS circuit or NMOS circuit. Also, in the presentembodiment, a driver integrated type where the driving circuit wasformed on the substrate was described, but this is not invariablynecessary. The driving circuit can also be formed on the outside ratherthan on the substrate.

1. A light-emitting device comprising: a substrate: a first electrodeover the substrate; an EL layer over the first electrode; and a secondelectrode over the EL layer, wherein the second electrode furthercomprises: a first film comprising a conductive inorganic material overthe EL layer, the first film including a pinhole; a second filmcomprising an organic material over the first film, the second filmformed so as to cover the pinhole; and a third film comprising aninorganic material over the second film.
 2. A light emitting deviceaccording to claim 1, wherein an end surface of the second film iscovered by the third film.
 3. A light emitting device according to claim1, wherein the conductive inorganic material is an alloy of aluminum andone of alkali metal and alkaline earth metal.
 4. A light-emitting devicecomprising: a first substrate: a first electrode over the firstsubstrate; an EL layer over the first electrode; a second electrode overthe EL layer; and a second substrate over the second electrode, whereinthe second electrode further comprises: a first film comprising aconductive inorganic material over the EL layer, the first filmincluding a pinhole; a second film comprising an organic material overthe first film, the second film formed so as to cover the pinhole; and athird film comprising an inorganic material over the second film,wherein an emission light from the EL layer is transmitted and emittedthrough the first substrate.
 5. A light emitting device according toclaim 4, wherein an end surface of the second film is covered by thethird film.
 6. A light emitting device according to claim 4, wherein theconductive inorganic material is an alloy of aluminum and one of alkalimetal and alkaline earth metal.
 7. A light-emitting device comprising: afirst substrate: a first electrode over the first substrate; an EL layerover the first electrode; a second electrode over the EL layer; and asecond substrate over the second electrode, wherein the second electrodefurther comprises: a first film comprising a conductive inorganicmaterial over the EL layer, the first film including a pinhole; a secondfilm comprising an organic material over the first film, the second filmformed so as to cover the pinhole; and a third film comprising aninorganic material over the second film, wherein an emission light fromthe EL layer is transmitted and emitted through the second substrate. 8.A light emitting device according to claim 7, wherein an end surface ofthe second film is covered by the third film.
 9. A light emitting deviceaccording to claim 7, wherein the conductive inorganic material is analloy of aluminum and one of alkali metal and alkaline earth metal. 10.A light-emitting device comprising: a substrate: a thin film transistorover the substrate; a first electrode electrically connected to the thinfilm transistor; an EL layer over the first electrode; and a secondelectrode over the EL layer, wherein the second electrode furthercomprises: a first film comprising a conductive inorganic material overthe EL layer, the first film including a pinhole; a second filmcomprising an organic material over the first film, the second filmformed so as to cover the pinhole; and a third film comprising aninorganic material over the second film.
 11. A light emitting deviceaccording to claim 10, wherein an end surface of the second film iscovered by the third film.
 12. A light emitting device according toclaim 10, wherein the conductive inorganic material is an alloy ofaluminum and one of alkali metal and alkaline earth metal.